It has become conventional to use steel joiner units in construction in some applications to decrease the on-site labor and to make a secure joint using the strength of the steel unit.
It has also been suggested that frameworks for certain applications, such as boat covers, wherein the structure may be dismantled and stored, have corner-joining elements of strong metal such as steel. See, for example, U.S. Pat. No. 3,740,084, issued on June 19, 1973, to K. O. Tellberg, entitled READILY DETACHABLE SELF-ALIGNING JOINT, and U.S. Pat. No. 4,076,431, issued on Feb. 28, 1978, to S. Burvall and entitled CONNECTING ELEMENT.
Such joining elements of the above patents are formed of a series of rectangular tubular metal sleeve sections, closed at one end to form end caps and firmly secured together by welding or forging or casting in one piece. These joiner members, by design, bear the entire weight of the received members and, thus, are of necessity made of tough, strong materials.